Set up in 1999, the TPS is a central opt-out register for those who do not wish to receive unsolicited sales and marketing calls.

The ICO found that Xternal should have screened the list of people it planned to call against the details of TPS subscribers, and failed to ensure that its telesales staff knew how to comply with the law.

The ICO will soon receive new powers, announced by the Government last year, to fine the directors of nuisance marketing firms as well as the companies themselves.

Ken Macdonald, head of regions at the ICO, said this will allow the organisation to take an even tougher stand against firms which intrude into people's lives.

“Nuisance marketing, whether it's by call to people's landline or mobile, or through spam texts, causes disruption, annoyance and, in the worst cases, serious upset,” Macdonald added. “We issue fines like these to firms behind nuisance marketing to send a clear message that such action will not be tolerated.”